In one of the scenes where they settle down for the night (not sure which one) you can plainly see Heather sitting there on the ground waving at the camera.. but at the same time she is being filmed with the B&W film AND you can hear her voice talking about something but yet her lips are not moving. It's like she was filming her twin!

It's called "editing". You can overlap sound that was recorded separately than film onto the film. In this case, a conversation was going on that was later dubbed onto the footage, creating this magical appearance of "not talking". It's a magic thing, this "editing".
Here's another nit-pick - the film is 1 1/2 hours long, yet it's night MORE THAN ONCE!! Several times, in fact! OOPS, WHAT A BLOOPER THAT IS!

This is to Critical_Critic. The Blair Witch Project is not a true story or based on a true story. The directors and film makers did go to lengths to explain that the whole story was fictional. The directors used the actor's real names, but the actors are safe and alive. Everything was made up, even the interviews, the legend, the Curse of the Blair Witch Project video, and the Blair Witch project Dossier. The actors would find notes posted in baskets on the trees from the directors, with tips on what to do next. Personally, I loved the BP. I think it is a very clever story and extremely realistic and believable. M.R.

That is called editing. But that wasn't the only time it happened. If you are a true Blair Witch fan like me, you will notice it happens when they are crossing the log the first time. Heather is walking across and you can clearly see that her lips are not moving yet she still can talk to Michael.

I also saw Heather crossing the log, talking without moving her lips. Maybe she is a ventriloquist.
Also, was I the only one who sat through that HORRID music(for lack of a better work) at the end of this picture to read that the charaters were FICTIONAL and any situations resembling this picture were purely coincidental? I thought this were a true story. Why would they need to display that disclaimer if it wasn't fiction.